The main point is, please do the basics. When designing a website, ensure controls with button-type behavior (interaction, affects the current page) are designed as buttons and regular text links (go to an external page, anchor on page, or external document) are designed like text links (such as blue underlined text).

When developing a website, ensure buttons are coded as buttons (the button or input element) and links are coded as links (the anchor element).

Here are some reasons why it’s so important:

accessibility and usability

a more robust website (support older user agents, non-JS, etc.)

lighter and less complex code

more consistent implementation so easier to maintain

Remember that for accessibility, no matter how much ARIA and trickery is done, there will mostly likely still be problems. When blurring the distinction between a button and a link, assistive technology (and/or the user) can be confused as to what’s what. View the beginning of this presentation by Derek Featherstone for a good example of this.

Button versus text link.

This advice sounds simple, but this elementary guideline is broken quite often; once you start to look, you’ll find it everywhere on the web, especially web apps. There’s no need to create confusion (the design) and to re-invent the wheel (the development). Sticking to the basics will make it easier for everyone, most importantly the user.